docs: def sniff_iface(f):
      """Ensure decorated function is called with a value for iface.
  
      If no iface provided, inject net iface inferred from unit private address.
      """
      def iface_sniffer(*args, **kwargs):
          if not kwargs.get('iface', None):
              kwargs['iface'] = get_iface_from_addr(unit_get('private-address'))
  
          return f(*args, **kwargs)
  
      return iface_sniffer